Sjogren Syndrome is an autoimmune inflammatory disease characterized by a particular form of dry mouth and dry eyes. It affects the lacrimal gland's ability to secrete tears and results in dry eye, salivary gland dysfunction, causing dry mouth and dryness in other mucous membranes such as the bronchial epithelium, the vagina and other mucosa.
This loss of tear and saliva fluids may result in characteristic changes in the eyes (called aqueous tear deficiency or keratoconjunctivitis sicca) and in the mouth with deterioration of the teeth, increased oral infection, difficulty in swallowing, and painful mouth. However, dry mucosa may also be due to other causes classified under the non-Sjogren Syndrome. The causes may be due to use of certain types of drugs, inflammation or infection, or hypothyroidism. Dry mucosa conditions due to any cause can affect both humans and animals such as mammals.
For the eyes, the lacrimal gland located in the orbit of the eye continuously secretes small amounts of tear fluid that are released onto the surface of the eye through very small ducts. Dry eye syndrome can be defined as a loss of tear fluid with accompanying abnormalities of the tear film. There are few objective signs of dry eye and importantly, discomfort which varies on an individual basis is the aspect that is most noticed by patients and which motivates them to seek help [1]. For severe cases, ocular surface damage and a loss of vision is not uncommon. Dry eye syndrome affects millions of people and its prevalence is estimated to be as high as 11˜22% of the general population with the prevalence in Asia greater than in the West [1]. It is more common in people over 55 years of age and in females; however, in Asia, dry eye is a factor in those over 45 [2]. The prevalence is also significantly higher in visual display terminal users and contact lens wearers.
The causes for dry eye syndrome are diverse; however, fundamentally it is due to a loss of fluid over the ocular surface and particularly the cornea. The cornea is the most important optical element of the eye and dry eye decreases good vision as well as the quality of life of the patient. The fluid layer over the ocular surface, called the tear layer, is some microns thick but has layers as follows: 1-outermost lipid layer, 2-middle aqueous layer and 3-inner mucin layer. Usually it can be classified into two major categories: tear secretion deficiency and excessive tear evaporation. Dysfunction of the lipid layer of the tear film leads to excessive evaporation of tears. A mucin layer deficiency often caused by vitamin A deficiency; however, except for developing countries, it is rare.
For therapeutic development by pharmaceutical companies for dry eye, non-Sjogren's dry eye is the primary target as it comprises the majority of these patients. At present there is only one actual therapeutic drug on the market, Restasis® from Allergan®. The reasons for this paucity in drug development arise primarily from the lack of objective measures of dry eye and therapeutic efficacy.
Diagnosis of dry eye syndrome is typically based on subjective symptoms, Schirmer test (evaluating quantity of tear fluid), tear break-up time (evaluating quality of tear film) and other less common clinical tests including fluorescein staining, Rose Bengal staining, measuring tear meniscus height, impression cytology, and others. Studies show that correlation is poor between clinical tests and symptoms and even between different clinical tests [3, 4]. This also makes a difficult scenario for the evaluation of therapeutic agents [5].
As such, new and improved methods of determining and diagnosing dry mucosa conditions such as dry eye are welcome.